Electrolytic Extraction of Transition Metals from Lithium-Ion Cathodes in Molten Hydroxide Salts

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We have developed an electrometallurgical recycling process that uses low melting temperature molten hydroxide salts to produce metals from lithium-ion battery materials. Existing commercial recycling processes typically use high temperatures, require high-purity reagents, and use coke as a reductant, which makes the processes expensive and CO2-emissions heavy1. Molten hydroxide salts can lower the required temperatures and emissions needed for extraction of critical materials from spent lithium-ion batteries.Molten hydroxide salts are water-tolerant, oxyanion-conducting, and can be used as electrolytes for electrochemical extractions2. This water tolerance is unique among molten salts and enables oxyanion-based electrochemical reactions through the Lux-Flood acid-base equilibrium: 2OH- ↔ H2O + O2- (1)Where water is the oxoacid and accepts oxyanions to form the hydroxide ion. Here, we leverage the unique properties of molten hydroxide electrolytes and demonstrate a one pot, two-step electrochemical extraction of critical metals from battery cathode materials. In the first step, lithium-ion cathodes are electrochemically reduced to form soluble oxides in the hydroxide melt. In the second step, the solubilized materials are reduced onto a separate cathode and recovered as an alloy. We will discuss test results for both process steps to recover Ni, Mn, and Co metal from both fresh NMC 622 and used cathode material (black mass). The effect of process conditions such as moisture content and operating parameters on the chemistry will be discussed. B. MAKUZA et al., “Pyrometallurgical options for recycling spent lithium-ion batteries: A comprehensive review,” J. Power Sources 491 February, 229622, Elsevier B.V. (2021); https://doi.org/10.1016/j.jpowsour.2021.229622.E. GÜRBÜZ et al., “Significance of Molten Hydroxides With or Without Molten Carbonates in High-Temperature Electrochemical Devices,” Front. Energy Res. 9 April, 1 (2021); https://doi.org/10.3389/fenrg.2021.666165.